This invention relates to the rolling of metal strip and in particular to the guiding of the strip to a downcoiler where it is coiled into a coil of a convenient size.
In FIG. 1 of the accompanying drawings, a conventional layout at the exist end of a hot strip mill is shown. Strip S leaving the last stand 1 of the hot strip mill passes along a run-out table where it is water cooled and it then pases through a pinch roll unit 3 which deflects the head end of the strip down to the downcoiler 5 where it is gripped and wound into the form of a coil. The plane containing the longitudinal axes of the rolls of the pinch roll unit 3 is set at a slight angle to the vertical so that the rolls turn the head end of the strip down between guiding deflector plates 7 to ensure that the head end is fed correctly to the mandrel of the downcoiler. Usually there are two or more downcoiles and strip can be coiled on either of these downcoilers. An additional pinch roll unit 3' is associated with a second downcoiler (not shown in FIG. 1).
In use, both pinch roll units and downcoilers are driven. When the downcoiler 5 is employed, it is first necessary to close the rolls of the pinch unit 3 to their working position so that the gap between the pinch rolls is of the order of, and usually slightly less than, the thickness of the incoming strip. The pinch rolls are rotated at a speed slightly faster than that of the incoming strip so that, when the head end of the strip is gripped by the pinch roll unit, a slight tension is imparted to the strip. Similarly, the downcoiler mandrel is rotated at a speed faster than the incoming strip in order to tension the strip. Once the head end of the strip has been gripped by the mandrel, the mandrel motor is controlled to apply a tension to the strip which is appropriate to the width and thickness of the strip. Just before the tail end of the strip leaves the last strand of the finishing mill, the tension applied by the pinch roll unit is increased until it is roughly equal to the tension being applied by the downcoiler mandrel so that the coiling tension in the strip is maintained. Side guides 9 are fitted on the run-out table, on opposite sides of the strip path, and these guides are normally set slightly wider than the strip width until the head end of the strip has been gripped by the downcoiler but, once tension has been established, the side guides are brought close to the edges of the strip to ensure that the coil on the mandrel is built up with straight sides.
When the second downcoiler is in use, the pinch rolls of the unit 3 are opened wide so that the head end of the strip passes unhindered between these rolls to the pinch roll unit 3' associated with the second downcoiler.
The side guides 9 suffer from rapid wear by abrasion from the edges of the strip. Wear plates are fitted to the guides and these can be changed rapidly. However, provision of a large number of wear plates is expensive and there is the further disadvantage that the edges of the strip can be damaged.